You seek a foundation for poker strategy. GTO is now considered to be the way forward. It’s underlying strategy is that every move be the one that maximizes expected value, EV. Therefore, I think that a complete understanding of EV is essential.
In the broadest sense, EV = Pr(W)*$win + Pr(L)*$lose
where
Pr(W) is the probability you win and the amount you win is $win
Pr(L) is the probability you lose and the amount you lose is $lose
Example: The pot is $100. Villain makes an all-in bet of $60. Should you call? You estimate your winning chances to be 30%.
EV = 0.30*(100+60) – 0.70 * 60 = 48 – 42 = 6
Since EV is positive, a call is reasonable given no other factors. Naturally, things are usually more complicated than this simple example but IMO having a good knowledge of the EV concept and its associated math is important.
You might find my free blog site Hold’em Mathology a good start toward achieving such knowledge.
https://holdemmathology.tumblr.com/post/181437891075